Reel mowers are well known pieces of outdoor power equipment used for cutting grass. Reel mowers are so named because they have at least one reel cutting unit that includes a bladed reel that rotates about a generally horizontal axis. Usually the blades of the reel are not themselves sharpened though in some instances they have been known to be sharpened. The primary purpose of the blades of the reel is to sweep the blades of uncut grass against the leading edge of a bedknife that is fixed on the frame of the reel cutting unit. The interaction between the blades of the reel and the bedknife shears the grass blades to cut the grass.
The geometry of a typical reel cutting unit usually places the bedknife beneath the rotatable reel and behind the centerline of the reel. In order to be effective in cutting grass, the reel and bedknife are adjusted so that the blades of the reel are either immediately adjacent to or in slight contact with the bedknife as the reel rotates. This provides a scissors type shearing action between the reel and the bedknife that is effective for cutting grass.
Many conventional bedknives are integrally formed from a single piece of steel that is then heat treated to increase hardness and durability. The tip of the bedknife is often sharpened to provide a cutting edge. Traditionally, such bedknives are quite strong and resistant to breaking from impact. However, such monolithic steel bedknives typically wear fairly quickly, requiring the cutting edge to be resharpened or the bedknife to be replaced. This is a disadvantage to single piece bedknives of this type.
Other known bedknives attempt to improve upon the wearability of single piece bedknives. These other bed-knives typically comprise a base that carries an insert at the tip thereof with the insert forming the cutting edge of the bedknife. In known insert bedknives, the base material comprises a less expensive, non-hardenable, low carbon steel (such as SAE 1018 or 1020). The insert comprises a much more expensive tool steel (such as M2). Neither the base material nor the tool steel are heat treated prior to their being joined together.
In manufacturing such insert bedknives, the base is provided with a seat at the tip thereof to receive the insert. The insert is placed into the seat with a copper brazing alloy being used at the interface between the insert and the seat. The insert is then brazed into place to integrally join the insert to the base by heating the copper filler at relatively high temperatures of approximately 2000° F. or so. This heating process both joins the insert to the base as well as heat treats the insert in situ to increase the hardness of the insert. This heating process does not, however, appreciably strengthen or harden the base material due to the fact that the base material is substantially non-hardenable even when heat is applied.
The Applicants herein have observed that conventional insert bedknives made as described above have relatively low yield strength in the base material. Yield strength is defined as the amount of force required to permanently deform the bedknife. As a result of this low yield strength, the Applicants herein have further observed two failure modes for conventional bedknives.
In the first failure mode, the bedknife strikes foreign objects during operation of the reel cutting unit, including but not limited to tree roots, drainage grates, bolts lying on the ground, yardage markers, etc. The impact with foreign objects is often significant to cause the bedknife to chip or fracture. This requires that the bedknife be repaired or even replaced if the area that is damaged is too large. This failure mode contributes to decreased customer satisfaction and higher warranty costs to the manufacturer of the reel cutting unit.
In the second failure mode, the bedknife can sometimes be deflected upwardly so that it interferes with the blades of the spinning or rotating reel. When a given blade then comes into contact with or strikes the bedknife, it is possible to peel off a portion of the hard edge of the bedknife. This is particularly true for bedknives that are extremely thin, such as those used on the reel cutting units of greensmowers. Such an occurrence completely destroys the bedknife requiring that the bedknife be totally replaced. It also can significantly damage the rotatable reel, further leading to other repair or replacement costs in conjunction with the reel.
Accordingly, there is a need in the reel mower art for a bedknife base or body with improved yield strength to minimize the aforementioned failures described above.